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Picture of Professor Tweed stompbox

Professor Tweed

This is a sweet sounding distortion pedal coming from Run Off Groove. This circuit is modeled after an old Fender Tweed amplifier but using JFETs instead of tubes. It's a quite simple build with trimpots for the bias of each transistor.

Layout & Transfer

Layout with board mounted pots and led to fit a 1590BB enclosure. I've routed the wire connections so that all wires going to the stompswitch are gathered at bottom center(ish) of the pcb. This makes for a nice bundle of cables located as close to the switch as possible.

Layout for Professor Tweed circuit pcb transfer for Professor Tweed

Transfer is 300 dpi.

Shown in the close up below are the three points on the board where measuring posts can be mounted. The location for these are not marked in the layout, the picture should help you locate them. These helps when biasing the JFETs. Using a standard 9 volt supply you want to bias all transistors drain to roughly 4.5 volt (half the supply voltage). More information at Run Off Groove, see link section.

Close up of bias measuring points

As a bonus you can see, in the middle of the board, the legs of the led sticking up. The led is mounted on the track side of the pcb and held to the enclosure by the board and helps keep the track side of the board from touching the enclosure. The board is held in place by the pots (bend the "legs" of the pots 90 degrees back).

Parts List

These are the parts you'll need.

Capacitors

ValueCount
470pF1
2.2nF2
4.7nF1
22nF3
1uF1
22uF2
100uF1

Pots

ValueCount
100k Log1
1M Log2

Resistors

ValueCount
1M1
68k1
1.5k2
220k1
470R1
10k2
22k1

Transistors

TypePosition(s)
MPF102 or 2N5457 or J201Q1
MPF102 or 2N5457Q2, Q3

Other Parts

Three (3) 100k trimpots. Led of your choise. Led resistor of your choise.

Gut Shot

This gut shot comes from my build of the Professor. It sounds really nice, but depending on the amount of dist you want you might want a booster before it, it's not a high gain circuit.

Gut shot of Professor Tweed build

Professor Tweed on Run Off Groove. Schematic and biasing information as well as a few other tidbits and alternative layouts.

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